1. Field of the Invention
The present invention relates to an electro-hydraulic variable valve lift system. More particularly, the present invention relates to an electro-hydraulic variable valve lift system which may realize asymmetric valve lift according to engine operation condition.
2. Description of Related Art
An internal combustion engine generates power by burning fuel in a combustion chamber in air media drawn into the chamber. Intake valves are operated by a camshaft in order to intake the air, and the air is drawn into the combustion chamber while the intake valves are open.
In addition, exhaust valves are operated by the camshaft, and a combustion gas is exhausted from the combustion chamber while the exhaust valves are open.
An optimal operation of the intake valves and the exhaust valves depends on a rotation speed of the engine. That is, an optimal lift or optimal opening/closing timing of the valves depends on the rotation speed of the engine.
In order to achieve such an optimal valve operation depending on the rotation speed of the engine, various researches, such as designing of a plurality of cam and a variable valve lift (VVL) that can change valve lift according to engine speed, a variable valve timing apparatus (VVT) that can change opening/closing time of a valve, an EHV (electro-hydro valve lift) have been undertaken.
A generally-used EHV apparatus applied to an internal combustion engine has identical valve lifts of intake valves per cylinder.
Recently a GDI (gasoline direct injection) engine has been used worldwide, and the GDI engine may improve compress ratio by injecting fuel into a cylinder directly and may suppress knocking.
However, in the GDI engine, air inflowing into a cylinder is not sufficient and thus air-fuel mixing is difficult, and noxious exhaust gas may be generated excessively.
For solving the drawbacks, asymmetric valve lifts for each cylinder is effective.
However, for having intake valve lift differently per cylinder, two independent EHVs are required for each valve and thus scheme may be complicated and production cost may be increased.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.